There are numerous patents relating to automatically disconnecting plugs. These disconnecting plugs differ in their structure and in strategies implemented through associated electrical ejecting circuits to cause the plug to disconnect upon the happening of a predetermined triggering event.
U.S. Pat. No. 4,045,106 (Borg 1977) discloses a male plug which has projecting prongs that are movable between an extended position and a retracted position. The prongs are spring biased to assume the retracted position, but are maintained in the extended position by a locking mechanism. Upon the triggering event occurring the locking mechanism is released and the prongs move to the retracted position, retracting from a female plug with which it is coupled. U.S. Pat. No. 5,645,439 (Nugent Jr. 1997) discloses a male plug which has an ejecting pin movable between an extended and a retracted position. The ejecting pin is spring biased to assume the extended position, but is maintained in the retracted position by a locking mechanism. Upon the triggering event occurring the locking mechanism is released and the ejecting pin moves to the extended position pushing a female plug end out of engagement with the male plug.
U.S. Pat. No. 5,831,802 (Ahmed et al 1998) teaches one skilled in the art to provide an energizing current to the ejecting circuit upon a substantial cessation of current flow by an appliance. U.S. Pat. No. 6,540,533 (Schreiber 2003) teaches one skilled in the art to monitor electrical power supply characteristics and provide an energizing current to the ejecting circuit when a predetermined sequence in rapid changes in electrical power supply characteristics are sensed.
In cold weather climates, motor vehicles are equipped with electric block heaters. These block heaters are plugged in when the vehicle is not in use. A problem commonly encountered is that of motor vehicle operators driving away without unplugging their block heaters.